Tungsten Oxide Ceramics Oxygen Filling Process

High oxygen partial pressure can inhibit the formation of oxygen vacancies in tungsten oxide ceramics, thereby affecting the mass transfer rate. However, a tungsten oxide ceramic sintered in an oxygen atmosphere has a relatively high density. The radius of oxygen ions is 0.14 nm, which is much larger than that of hexavalent tungsten ions.

The mobility of oxygen ions in the crystal lattice of tungsten oxide ceramics is inferior to hexavalent tungsten ions. Therefore, oxygen ions have a great influence on the mass transfer rate in the sintering process. A certain amount of oxygen vacancy concentration can promote the sintering of tungsten oxide ceramics. When the tungsten oxide ceramic is sintered in an oxygen atmosphere, the generation of tungsten oxide oxygen vacancies is suppressed but does not stop. The generation of oxygen vacancies in tungsten oxide ceramics and the process of oxygen atoms filling in oxygen vacancies are dynamic equilibrium processes.

After the formation of oxygen vacancies in the grain boundary of tungsten oxide, the oxygen atoms in oxygen fill it up. This rate is much faster than the oxygen atoms in other locations in the tungsten oxide lattice filled by diffusion. Therefore, a tungsten oxide ceramic sintered in an oxygen atmosphere has a relatively high density. The vacuum sintering of tungsten oxide ceramics has a large concentration of oxygen vacancies. If placed in an oxygen atmosphere for the second time, the oxygen atoms fill up the oxygen vacancies, which can increase the grain growth and density. However, the growth rate of the tungsten oxide grains is inversely proportional to the original radius of the tungsten oxide grains. Therefore, the tungsten oxide ceramics obtained by the heat treatment in oxygen after vacuum sintering have large crystal grain sizes without the sintering of air and oxygen.

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